Re: [ovirt-devel] [Spice-devel] ovirt-guest-agent behavior on disconnect

On 09/30/2015 10:03 PM, Barak Azulay wrote: > > > Barak > > On Sep 30, 2015, at 10:04, Michal Skrivanek > <<mailto:michal.skrivanek@redhat.com>michal.skrivanek@redhat.com> wrote: > >> >> On Sep 25, 2015, at 19:40 , David Mansfield >> <<mailto:ovirt@dm.cobite.com>ovirt@dm.cobite.com> wrote: >> >>> [cross-posted to <mailto:devel@ovirt.org>devel@ovirt.org and >>> spice-devel(a)lists.freedesktop.org >>> <mailto:spice-devel@lists.freedesktop.org>] >>> >>> Hi oVirt Devs, >>> >>> I'm here from the spice-devel list where we were discussing some >>> changes to the behavior of the spice guest agent reacting to a user >>> disconnect (of the spice console). >> >> Hi David, >> great, any enhancement is good! Vinzenz, please add more details to >> my guesses below:) >> >>> >>> Some information about how the ovirt-guest-agent works would be >>> informative if you can spare a minute. >>> >>> The functionality being discussed is locking the user session in the >>> VM when the user disconnects from spice (either intentionally or >>> unintentionally). > > What OSs are we talking about (the behavior is significantly different > and each pose different challenges. > > >>> >>> Also, peripherally, how does oVirt ensure secure access by >>> authorized users of a VM and prevent "over-the-shoulder" snooping >>> (spice graphics session stealing) or other forms of information leak >>> from a VM shared by multiple users. > > We have several mechanisms to ensure that: > 1 - ticketing system managed by the engine, so permissions are checked > on the ovirt-engine, if a user has permissions to connect to the vm > than the engines sends vdsm the ticket (and it sets the ticket to the > spice server ... Through libvirt), and than the client receives this > ticket to present to the spice server on connect (of course this > ticket has time expiration) > 2 - every time the client disconnects we receive an event and > immediately send lock desktop command to the guest (through the > ovirt-guest-agent). This is implemented both for win and Linux but for > a Linux guest for that to work one must work on run level 5. > 3 - anyway since this is racy , in order to avoid session theft we do > not allow a second user to connect to a vm when the first user > disconnected, the second user will be able to login only after the cm > was rebooted. > > > > >>> >>> So here are some questions: >>> >>> Can a VM be "shared" by multiple users in oVirt at all? Are there >>> known security issues that would make this a non-recommended or >>> fundamentally un-securable setup? >> >> normally no, there is a semi-supported hook to allow that with VNC >> (and even that is slightly broken IIRC at the moment), but in general >> we do want so support that for specific usecases > > The question is not clear enough, > > In case you mean simultaneously (2 users) than the above answer is > relevant. > In case you mean sequential ... Than the answer is explained above , > and yes we allow a vm to be shared among several users or groups. > > >> >>> >>> Does the oVirt agent lock the session on disconnect? Always / >>> unconditionally? > > IIRC It will always try to lock, but we can not guarantee that the > operation actually succeeded (long story ...) > > >>> If it's configurable, where does the configuration reside - in the >>> vm guest, on the vm host (/engine) or on the client? >> >> it's oVirt management UI configuration, it changes the host's >> behavior on spice disconnect per VM >> >>> >>> Does the oVirt agent lock all sessions or the current active session? >> >> just the active AFAIK > > On windows its implemented only for desktop OSs (... Xp ...win7 ...) > we lock only the interactive session, for win server this is not > supported , in fact we do not install the SSO mechanism at all because > it works differently for those OSs (w2k3 , 2008, 2010) > > On Linux it's a bit more complicated , but we find the session of the > user we know connected to the vm ... And send the lock command. Actually not completely correct, currently we only lock the first, we don't try to match the user, the current assumption is that we only allow one user per VM therefore there can't be more than one active session. That said, that's how it is currently implemented. Not that this is the best way. > > As explained above since there is no guarantee for that to succeed > than we do not allow other users to connect till the cm is rebooted. > > >> >>> >>> How does it lock the sessions? I've looked at the code and it >>> appears '/usr/bin/loginctl lock-sessions' is being used on machines >>> it's provided on and something more complicated on older boxes. >>> Does the user have a way to customize this behavior? and if so, is >>> it VM guest, VM host or client configuration? > > > AFAIR this is not configurable ... But Vinzenz should be able to give > an accurate answer The only configuration you can do as of ovirt/RHEV 3.6 is that you are now able to say to perform one of the following actions on console disconnect: - Lock the screen - Logout the current user - Reboot the VM - Shutdown the VM - Do nothing